1. Field of the Invention
This invention relates to a circuit substrate with a built-in coil in which a coil component serving, for example, as a transformer or a choke coil is included.
2. Description of the Related Art
Along with the recent reductions in the size and weight of electronic equipment, power supplies such as DC-to-DC converters are also being reduced in size, particularly in regard to their thickness. FIGS. 7 and 9 show a side view and a perspective view of a conventional DC-to-DC converter. A DC-to-DC converter 50 has a circuit substrate 51, a coil component 52 fixed on the back surface of the circuit substrate 51, and electronic components 53 and a circuit pattern 55 provided on the front surface of the circuit substrate 51. Separate clip-type terminals 54 are mounted on edges of the circuit substrate 51 in contact with the circuit pattern 55. The circuit substrate 51 is made of a material such as alumina. The coil component 52 is formed by sandwiching a flat coil between sheet-shaped magnetic materials made of amorphous alloy foil. The electronic components 53 include field-effect transistors, diodes, integrated circuits, resistors, and so forth. The electronic components 53 and the circuit pattern 55 form a circuit.
The overall thickness of the above-described DC-to-DC converter is increased by the thickness of the coil component 52 which is fixed on the back surface of the circuit substrate. Thus, the ability to further reduce the thickness of the circuit substrate 51 is to some extent limited. For this reason, the overall thickness of a power supply such as a DC-to-DC converter is difficult to reduce.